A C3H osteosarcoma model has been developed which permits the quantitation of viable tumor cells metastasized to the lungs of individual animals after the primary growth is removed by surgery. Tumor cell quantitation is achieved by monitoring the levels of alkaline phosphatase produced by the neoplasm. In animals bearing as much as 2 g of tumor (5 x 10 to the 8th power cells) in the thigh, treatment with cyclophosphamide in optimal schedules and dose has achieved 99.99% tumor cell kill but no cures. We propose to use this model to 1) assess the effects of combinations of surgery, irradiation and chemotherapy and define the requirements and schedules for reducing tumor cell numbers in vivo to suitable levels for immunotherapy, 2) develop attenuated clones of tumor cells by tissue culture which can confer resistance in syngeneic animals for the purpose of generating tumor specific killer cells, 3) determine the time when passive immunotherapy must be given and establish the killer to target cell ratio which must be achieved in vivo in animals whose tumor cell numbers have been reduced by prior surgery, irradiation or chemotherapy, 4) determine the antigen(s) in the various attenuated clones which confer immunity in syngeneic mice.